1. Field of the Invention
The present invention relates to a method for preparing dilute polymer solutions and in particular to a method for preparing dilute aqueous polymer solutions of the type used in secondary and tertiary oil recovery processes.
2. Description of Related Art
Various apparatus and methods for preparing aqueous polymer solutions, including aqueous solutions of partially hydrolyzed polyacrylamides, have been proposed. U.S. Pat. No. 2,820,777 discloses a one-step batch method for simultaneously polymerizing and hydrolyzing acrylamide monomer in a single reaction vessel. Two solutions are pumped at an equal volume rate into the reactor. The first solution comprises acrylamide monomer and water and the other comprises a polymerization catalyst, an alkali metal hydroxide, and water. Although the properties of the polymer product may be a function of the proportional amount of reactants and the reaction conditions, as the patent suggests, it is virtually impossible to predictably produce a specific polymer using this batch method because of inherent process control difficulties. Therefore, the method is unsuitable for preparing aqueous polymer solutions used in secondary and tertiary oil recovery processes. Such processes require polymers having predictable properties to meet the performance demands of an oil-bearing formation.
U.S. Pat. No. 4,110,521 is directed to a method for the continuous preparation of aqueous polymer solutions. The method is relatively complex and costly because it requires a large number of static mixers, pumps and temperature controls. As a result, it is impractical and unsuitable for on-site preparation of aqueous polymer solutions used in secondary and tertiary oil recovery processes.